The prostaglandins are a potent class of biologically active lipid derivatives that play a crucial role in the inflammatory response. The inflammatory response is a localized tissue response to injury or other trauma characterized by pain, heat, redness and swelling. Prostaglandins mediate this response by inhibiting platelet aggregation, increasing vascular permeability, increasing vascular dilation, inducing smooth-muscle contraction and causing the induction of neutrophil chemotaxis. Because of their central role in mediating the inflammatory response, significant efforts have been directed toward elucidating compositions that are capable of inhibiting the biosynthesis of prostaglandins.
Toward that end, prostaglandin biosynthesis has been extensively characterized. Prostaglandins are a group of oxygenated fatty acids that are generally derived from arachidonic acid. The biosynthesis of prostaglandins from arachidonic acid occurs in a three step process that includes 1) hydrolysis of arachidonic acid from phospholipid precursors catalyzed by a phospholipase A2; 2) cyclooxygenase (“COX”) catalyzed oxygenation of arachidonic acid to prostaglandin G2 (“PGG2”). This COX catalyzed reaction is the first committed and rate limiting step in prostaglandin synthesis; and 3) conversion of prostaglandin G2 to the biologically active end product, prostaglandin, catalyzed by a series of synthases and reductases. Upon their synthesis, prostaglandins exit the cell and act in a hormone-like manner by affecting the target cell via G protein linked membrane receptors.
Inactivation of the COX enzyme is a natural target as a means to inhibit prostaglandin production due to this enzyme's pivotal role in the prostaglandin biosynthetic pathway. It is now known that two gene products possessing COX enzyme activity are expressed, termed COX-1 and COX-2. COX-1 was the first discovered isoform and is constitutively expressed in most tissue types. Because it is constitutively expressed, COX-1 is available to participate in activities requiring a rapid physiological response and causes the production of prostaglandins involved in “house-keeping” functions. For example, COX-1 is responsible for acute production of prostaglandins that regulate vascular homeostasis, maintain gastrointestinal integrity, and maintain kidney function. Thus, COX-1 activity is responsible for the synthesis of prostaglandins required for the maintenance of several cell types.
COX-2, on the other hand, is a recently discovered isoform that is inducibly expressed in response to numerous stimuli such as bacterial lipopolysaccharides, growth factors, cytokines, and phorbol esters. In addition, COX-2 is only expressed in a limited number of cell types including monocytes, macrophages, neutrophils, fibroblasts and endothelial cells. COX-2 expression, but not COX-1 expression, has been shown to increase in rheumatoid synovial tissue. Contrastingly, COX-2 expression is inhibited in response to glucocorticoids and by anti-inflammatory cytokines. Thus, based upon these observations, COX-2 has been shown to be the isoform responsible for mediating the production of prostaglandins that participate in the inflammatory response and inflammatory related disorders. In addition, COX-2 has also been shown to participate in certain cancers, Alzheimer's disease, atherosclerosis, and central nervous system damage resulting from stroke, ischemia and trauma.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are also utilized as a means to reduce effects associated with the inflammatory response. The principal pharmaceutical effects of NSAIDs are due to their ability to prevent COX activity resulting in the inhibition of prostaglandin synthesis. Inhibition of prostaglandin synthesis by NSAIDs is anti-pyretic, analgesic, anti-inflammatory, and anti-thrombogenic. However, administration of NSAIDs may also result in severe side effects such as gastrointestinal bleeding, ulcers and incidence of renal problems.
There is a great need for new drugs that modulate COX activity, as well as assays to facilitate the discovery of such drugs. This invention meets this need.